1. Field of the Invention
The present invention relates to a driving of a switched reluctance motor (hereinafter, referred to as xe2x80x98SR motorxe2x80x99), and in particular to a driving device for an SR motor which can detect a position of a rotor of the SR motor by using a smaller number of sensors than phases, and which can drive the SR motor on the basis of the detected result.
2. Description of the Background Art
In order to exactly drive the SR motor, it is necessary to detect a position of a rotor of the SR motor. For this, sensors as many as phases are required. A speed of the rotor can be controlled by driving the rotor according to a result detected from the sensors.
For convenience"" sake, a three phase SR motor will now be exemplified. FIG. 1 is a circuit diagram illustrating a driving device of a conventional SR motor. Reference numeral 10 denotes a microprocessor, 20 denotes a switching mode power supply (hereinafter, referred to as xe2x80x98SMPSxe2x80x99), 30 denotes a driving circuit, and 40 denotes a position detection unit. The driving circuit 30 includes first to third driving units 31, 32, 33. The first to third driving units 31, 32, 33 apply a current respectively to an A phase winding La, a B phase winding Lb and a C phase winding Lc of a stator of the motor. The position detection unit 40 includes first to third photo sensors Sa, Sb, Sc detecting a position of each phase of the rotor, and three switching transistors Q7, Q8, Q9 corresponding to the operation of the three photo sensors Sa, Sb, Sc, and outputting a predetermined voltage (5V) to the first to third driving units 31, 32, 33 of the driving circuit 30, respectively. On the other hand, a sensor disc with a slot (not shown) is inserted into the SR motor for the operation of the photo sensors Sa, Sb, Sc.
The operation of the conventional driving device for the SR motor will now be described.
The microprocessor 10 outputs a control signal to the SMPS 20. The SMPS 20 outputs a direct current voltage having a predetermined level to the driving circuit 30 according to the control signal. The direct current voltage is converted by a capacitor C1 and a resistance R1, and applied to the first to third driving units 31, 32, 33. In this state, when the position of the rotor is detected by the position detection unit 40, one of the first to third driving units 31, 32, 33 is operated according to the detected result. Accordingly, the current is applied to the A phase, B phase or C phase winding of the stator, thereby rotating the rotor.
For example, when the first photo sensor Sa is turned on, the switching transistor Q7 is turned on. Thus, a voltage of 5V is applied to a lower switching transistor Q4 of the first driving unit 31. Accordingly, the lower switching transistor Q4 is turned on, and an upper switching transistor Q1 is also turned on, thus forming a current path consisting of the upper transistor Q1, the A phase winding of the rotor and the lower switching transistor Q4. The direct current voltage from the SMPS 20 is applied to the A phase winding La, and thus the rotor is rotated. When the rotor is rotated by a predetermined angle, the first photo sensor Sa is turned off, and the second photo sensor Sb is turned on. The switching transistor Q8 is turned on by the On state of the second photo sensor Sb, and thus a lower switching transistor Q5 and an upper switching transistor Q2 of the second driving unit 32 are sequentially turned on. Accordingly, the direct current voltage from the SMPS 20 is applied to the B phase winding Lb of the stator, and thus the rotor is constantly rotated. On the other hand, a magnetic flux generated to the A phase winding La is removed by two free wheeling diodes D1, D2 of the first driving unit 31, thereby smoothly rotating the rotor.
The above-described position detection and driving steps are repeatedly performed, and thus the rotor is constantly rotated. On the other hand, in order to vary a rotation speed of the motor, the SMPS 20 may vary a level of the direct current voltage according to the control signal from the microprocessor 10. The rotation speed of the rotor is varied according to the level of the direct current voltage.
However, the conventional driving device for the SR motor requires the position detection sensors such as the photo sensors as many as the phases in order to detect the position of each phase of the rotor. The position detection sensors are high priced. In addition, added is a step for installing the position detection sensors to the SR motor. In case any of the position detection sensors is out of order, the SR motor cannot be normally operated.
Accordingly, it is an object of the present invention to drive a switched reluctance (SR) motor by using a smaller number of position detection sensors than phases.
In order to achieve the above-described object of the present invention, there is provided a driving device for a switched reluctance (SR) motor, including: a position detection unit for detecting a position of a rotor of the SR motor by using one position detection sensor; and a microprocessor for aligning the rotor by sequentially outputting a plurality of control signals at an initial stage of a starting of the SR motor, and for sequentially outputting the plurality of control signals according to a result detected from the position detection unit after starting the SR motor.